Microbalance with low-friction bearing



May 25, 1965 KANESUKE IWASAKI 3,185,231

MICRO BALANCE WITH LOW-FRICTION BEARING Filed Feb. 121 1964 2 Sheets-Sheet 1 F IG.

l L 2 3 I Kanesuke. Iwusaki bi Inverfior- May 25, 1965 KANESUKE IWASAKI 3,135,231

(v MICROBALANCE WITH LOW-FRICTION BEARING v Filed Feb. 12, 1964 2 Sheets-Sheet 2 Kancsuke Iwasaki y Invcwfor fiarne s United States Patent Japan Filed Feb. 12, 1964, Ser. No. 344,270 Claims priority, applgcsation-sgapan, Feb. 15, 1963,

3 Claims. 61. 177-190 There has been recently required an improvement in the art of measurements, particularly a rapid progress in efficiency of a balance as a weighing tool in the chemical, medical, pharmaceutical and other fields. The present situation is that only minor but not substantial progress has been made in the art up to now.

For, according to the present technical level with respect to a balance mechanism using a knife edge as a fulcrum, it is usually required to sacrifice a range of effective weights in one or two figures in an attempt to improve the sensitiveness of a balance in the degree of one figure. This is caused by the fact that the initial weight loaded on a knife edge in the case of a microbalance may be still about 30 grams, even if the balance mechanism of said microbalance is reduced in weight.

After my extensive studies, it has been concluded that the sensitiveness of a balance depends upon the degree of a maximum static rolling frictional force F between the center knife edge and the bearing therefor. Now, the rolling motion of a cylinder on a plane surface will be defined by the equation wherein ,u is a constant determined by the material of a knife edge as well as the polishing techniques therefor. In order to reduce the maximum static rolling frictional force F, variables W and 7 should be decreased. In the prior art, an attempt has been directed to improve the sensitiveness by decreasing the Value of W, e.g. by using a beam and other operating parts made of a light metal and sacrificing a maximum weighable amount. In the art, it is further common to use a knife edge as sharp as possible, because of a simple assumption that such knife edge would serve to improve the sensitiveness of the balance.

It has come to my attention that when a knife edge having been polished to as sharp an edge as possible is used, the load impressed to the bearing for the knife edge becomes greater. This naturally means that both the numerator and denominator, W and 'y, decrease in parallel and accordingly the value of F can not be so reduced. Further, with respect to the maximum static rolling frictional force, it has been considered that in a balance of such type where the weight impressed on the knife edge is constant, the increased diameter of curvature of the central knife edge will increase the area through which the knife edge is in contact with the hearing, while reducing the load per unit area of the knife edge. This is apparently equivalent to decreasing the value of W. 2

Even if a knife edge and the bearing therefor are made of the hardest material now available and considered to be the highest in hardness, e.g. sapphire or ruby, the knife edge still suffers from deformation or injury, because both are used under the condition near the limit of pressure resistance of their material, considering the length of effective contact between the knife edge and the bearing. Sometimes, such deformation or damage may take place even when no load is placed on a pan. Calculation of the radius of curvature, or the length of ef- "ice fective contact, of the knife edge also shows that the above-mentioned assumption is true. In spite of the prior knowledge, I have found that none of the known materials would be an ideal rigid mass and therefore it is impossible to neglect the curvature of a material when used as a knife edge.

An object of the present invention is to obtain an increase in weighable maximum limit without sacrifice of the sensitiveness of a balance. Another object of the present invention is to reduce the apparent total weight of a beam and other balance mechanism placed on a knife edge by utilizing a repellent force between each of two pairs of the magnets arranged opposite to each other whose opposing poles are of the like type.

Still another object is to provide a balance the sensitiveness of which is substantially constant over the whole range of weighable amounts. Other objects, features and advantages of the invention will be apparent from the description and claims which follow.

In accordance with the present invention, there is provided a balance, comprising a pair of cylindrical permanent magnets individually fixed at a right angle to the central axis passing through the fulcrum and on opposite sides of a beam, the radius of movement of said magnets being equal to the locus of movement of the center of gravity due to the slant of the beam which oscillates around the fulcrum of the beam of the balance or to a distance in such a range that the center of gravity is located below the fulcrum. There is also provided an other pair of magnets individually fixed at a suitable distance below, and in the opposing relation to the first pair of the magnets so that each of two pairs of the magnets arranged opposite to each other have like poles at their opposing end portions.

The balance of the present invention may further comprise an elastic member interposed between a bearing supporting a knife edge and a pedestal, said elastic member being placed movably in a downward direction, without horizontal deviation, in response to an increase in weight of the load. In the operation of the balance of the invention, increased weight imposed on the edge bear ing plate may cause the horizontally downward movement of the bearing and the pedestal, so that when the distance between each of two pairs of the opposing magnets is shortened, the repellent force is strengthened until it serves in compensating for or in minimizing an increase in the weight load on the knife edge.

In the accompanying drawing representing an embodiment of the present invention, FIG. 1 is a front elevation of said embodiment and FIG. 2 is a side elevation of an essential part of said embodiment.

Now, the constitution of the present invention will be explained in reference to the accompanying drawing.

In FIG. 1 there is shown a balance using a round beam 1, which has as a central axis a vertical line passing thru the fulcrum, that is, a pointed end of a knife edge 2. Cylindrical magnets 3, whose radius is as great as that drawn by the center of gravity of the beam 1 when the beam is slanted centering around the fulcrum, are fixed to either side of the beam 1. Below the end portions of the respective magnets 3 there are provided magnets 6 which both are fixed to a yoke 5 fastened on a pedestal 4. The respective magnets 6 are positioned opposite to the corresponding magnets 3 with suitable space intervening, so that the end portions of each pair of the opposing magnets 3, 6 are like poles.

An elastic member 10 is interposed between the lower surface of an edge bearing plate support 8, supporting an edge bearing plate 7, and a pedestal 9.

Foradditional information, a numeral 11 designates a metal fixture which is fixed to a scale plate 12 graduated to indicate a minute quantity of weight, and its =3 top portion is fixed to edge designates 8; and a numeral 13 means a pointer.

As the present invention is constituted as above de scribed, when the balance is put in motion without load, the total weight of the beam, the magnets and other movable balance members is imposed upon the fulcrum, the pointed end of the knife edge 2. However, the repellent force occurring between the like poles of each pair of the opposing magnets decreases said weight, and the effective point of the repellent force is located at the center of gravity. Therefore, shifting of the center of gravity does not take place, and the performance of a balance of the present invention is not adversely influenced. As the weight imposed upon the pointed end of the knife edge is reduced, the knife edge may be used up to the state near the limit hardness of its material and its durability may be improved.

It is possible for the load to be augmented up tothe limit of pressure resistance of the knife edge material. When the equilibrium is obtained by placing the load on one pan and weights on the other, so much weight further imposed upon a pointed end of the knife edge causes the compression of the elastic member, with the result that the distance between the opposing magnets is diminished and the repellent force due to magnetism is increased to compensate for or subtract from the added weight at the pointed end of the knife edge.

When both the opposing magnets as used are permanent ones having almost equal magnetism, the repellent force is strengthened in inverse proportion to the second power of the distance between said magnets, so that the load at the edge point may be kept constant within the range of weight which the balance can measure. This leads to the following advantages that the flexure in the round beam may be negligible and that, with reference to this advantage, a balance may be given a substantially constant sensitiveness by the constitution of the present invention.

As will be apparent from the above description, the weight imposed upon the edge bearing plate of the balance of the invention may be kept approximately constant with or without a load being placed thereon, and this fact will result in a decrease in frictional resistance, an increase in effective weight and an enlargement of the range of weight of a load which may be measured.

What I claim is:

1. A balance comprising a pair of cylindrical permanent magnets individually fixed at a right angle to the central axis of the beam passing through the fulcrum and on to either side of a beam, the radius of movement of said magnets being equal to the locus of movement of the center of gravity due to the slant of the beam centering around the fulcrum of the beam of the balance so that the center of gravity locatesbelow the fulcrum, and another pair of magnets individually fixed at a suitable distance below, and in the opposing relation to, the corresponding first magnets, so that each of two pairs of the magnets arranged each opposite to other have like poles at their opposing end portions.

2. A balance as claimed in claim 1, further comprising an elastic member interposed between an edge hearing plate supporting an edge bearing plate and a pedestal, said elastic member being movable downwardly, without horizontal deviation, in response to an increase in weight of the load.

3. In a balance comprising a pedestal, an edge bear ing plate support thereon, a knife edge on said support, a beam fixed to said knife edge, weighing pans on opposite sides of said knife edge, the improvement which includes a first pair of magnets on opposite sides of said knife edge and fixed to said beam, a second pair of magnets spaced vertically from said first pair and mounted on said pedestal, the poles at the free ends of said first pair of magnets being of the same polarity, respectively, as the adjacent poles of the magnets of the second pair.

4. A balance according to claim 3 characterized in that the magnets of the first pair are horizontal and cylindrical.

5. A balance according to claim 3 characterized in that said beam is resiliently mounted on said pedestal through said plate support.

6. A balance according to claim 3 characterized in that the magnets of said second pair are vertically mounted on said pedestal.

7. A balance according to claim 3 characterized in that said second pair of magnets are below said first pair.

8. A balance according to claim 3 characterized in that the adjacent poles of said magnets are south on one side and are north poles on the other side of said knife edge.

References Cited by the Examiner UNITED STATES PATENTS 238,841 3/81 Brackett 308-2 1,717,462 6/29 Nagaoka et al. 177-185 1,974,940 9/34 Wood 177-195 FOREIGN PATENTS 58,734 11/53 France. 922,673 1/55 Germany.

LEO SMILOW, Primary Examiner. 

1. A BALANCE COMPRISING A PAIR OF CYLINDRICAL PERMANENT MAGNETS INDIVIDUALLY FIXED AT A RIGHT ANGLE TO THE CENTRAL AXIS OF THE BEAM PASSING THROUGH THE FULCRUM AND ON THE EITHER SIDE OF A BEAM, THE RADIUS OF MOVEMENT OF SAID MAGNETS BEING EQUAL TO THE LOCUS OF MOVEMENT OF THE CENTER OF GRAVITY DUE TO THE SLANT OF THE BEAM CENTERING AROUND THE FULCRUM OF THE BEAM OF THE BALANCE SO THAT THE CENTER OF GRAVITY LOCATES BELOW THE FULCRUM AND ANOTHER PAIR OF MAGNETS INDIVIDUALLY FIXED AT A SUITABLE DISTANCE BELOW, AND IN THE OPPOSING RELATION TO, THE CORRESPONDING FIRST MAGNETS, SO THAT EACH OF TWO PAIRS OF THE MAGNETS ARRANGED EACH OPPOSITE TO OTHER HAVE LIKE POLES AT THEIR OPPOSING END PORTIONS. 